Tangential cutting inserts are often used with milling cutters such as slotting cutters or extended flute cutters. Examples of such cutting inserts are found in U.S. Pat. No. 3,416,209, U.S. Pat. No. 3,490,117, U.S. Pat. No. 3,701,187 and U.S. Pat. No. 4,790,693.
U.S. Pat. No. 6,238,146 discloses an improved tangential cutting insert. The cutting insert has a body with an operative front surface associated with upper and lower main cutting edges. Each of the main cutting edges is connected, through corner edges, to side auxiliary cutting edges. The main cutting edges, side auxiliary cutting edges and corner edges have a rake surface associated therewith in the front surface of the cutting insert.
The two main cutting edges of the cutting insert of '146 each comprise two lateral component cutting edges giving rise to four right hand cutting edges and four left hand cutting edges. However, only one lateral component cutting edge of a given main cutting edge can be used at a time as a cutting edge to machine a 90° shoulder. If the cutting insert of '146 were to use the entire length of a main cutting edge to machine an extended shoulder, i.e., using two adjacent lateral component cutting edges, the result will not be a straight 90° shoulder.